Bragg Gratings Slopes Shape and the Measurement Error of the Microwave Signals Instantaneous Frequency

Modern radio engineering methods for measuring instantaneous frequency of microwave signals (IFM-systems) are characterized by low noise immunity, the fundamental possibility of operating only in a narrow frequency band with multichannel spectral expansion, and the cumbersomeness of devices for their technical implementation. Photonic methods for measuring the instantaneous frequency, based on the procedures of its measuring conversion in the optical range and including, as a rule, the processes of modulation, dispersion discrimination with frequency-amplitude conversion and photodetection, are the most promising, since they have significant advantages over radio engineering – a wide bandwidth of measured frequencies, low losses and immunity to electromagnetic interference, low weight, volume, the ability to work in a wide range of climatic conditions. At the present stage of development of photonic methods, FBG is used as one of the main devices for instantaneous frequency – dispersive discrimination. The advantages of the FBG are in the unique conversion of the measured frequency into the amplitude of the reflected or transmitted radiation of an optical carrier modulated by a radio signal, and in the possibility of simple manufacture. The main disadvantages of the IFM-systems with FBG are the monotonicity of the characteristics of the measuring conversion in the region of the central wavelength and the high level of response of the gratings to temperature and deformation. To overcome similar limitations in sensor and telecommunication systems, the use of special FBG structures are aimed. In this paper we analyze the measurement error of the microwave signals instantaneous frequency in FBGs with Gaussian, concave and triangle forms in beat-based IFM-systems for multi-signal registration.